The main objectives of the present study are (1) the assessment of age-related differences in drug sensitivity on psychomotor and cognitive tasks and (2) the evaluation of the usefulness of measuring performance as a function of difficulty level in assessing drug effect. The long-term goal related to these aims involves the development of more sensitive, reliable and practical techniques of evaluating drug reaction in older adults. These methods can ultimately be used with patients in order to provide a more informed basis for prescribing and management of drug usage in the elderly. By being able to assess the degree of undesirable impairment of cognitive and psychomotor functions, such a task battery can be used to predict the susceptibility of older individuals to the side effects of psychotropic medications and thus result in the safer utilization of these substances in a particularly vulnerable population. A crossover experimental design will be used in two studies to examine the effects of diazepam and lorazepam on psychomotor and cognitive performance at two age levels. Placebo or drug will be administered in a double-blind, counterbalanced design to groups (N=16) of young and elderly subjects. During the initial phase subjects will be trained to a plateau level of performance on several tasks. During a subsequent test session subjects will perform a predrug battery, ingest the drug and repeat the tasks several times over a 5 1/2-hour period. The tracking and digit symbol substitution tasks will consist of several forms, representing varying levels of difficulty. Drug effect for each age group will be interpreted in terms of performance plotted as a function of difficulty level. Analyses of slopes and intercepts of these curves will be conducted to determine age differences in sensorimotor, psychomotor, visual encoding and memory processes.